Ink reservoirs for use with writing instruments such as the rollerball pen, porous tipped pens, highlighters and marking pens ("Magic" markers) have conventionally been formed of a fibrous bundle compacted together into a cylindrical or rod-shaped unit having longitudinal capillary passageways among the fibers which serve to hold and release the ink (see, for example, U.S. Pat. Nos. 4,729,808; 4,286,005; and 4,354,889). The reservoirs resemble cigarette filters in form, density and texture. The fibers of these reservoirs are typically either cellulose acetate (for water-based inks) or polyester (for toluene-based inks). Cellulose acetate is currently more expensive than polyester on a weight basis. It is believed that cellulose acetate fibers are extensively used for making ink reservoirs because of the ready availability of high denier bundles in the form of "filter-tow", which is sold to the makers of cigarette filters. Polyester is used with non-water-based inks because cellulose acetate is attacked by many common non-polar solvents.
Ink reservoirs known in the prior art which are made of polyester fibers have fiber cross-sections which are conventional (i.e., substantially round).
It would be desirable to have an ink reservoir containing polyester fiber that is suitable for use with water-based inks. Polyester fibers having non-conventional cross-sections (i.e., substantially non-round) are known in the art but are heretofore unknown to be useful in ink reservoirs (e.g., see U.S. Pat. Nos. 4,639,397; 4,590,032; 2,828,528; and 4,008,044). We have discovered an ink reservoir suitable for use with aqueous or water-based inks which makes use of polyester fibers containing grooves which extend along the length of the fiber (i.e., axially).